When a disc is loaded in an optical drive, by means of a tray or not, the first step to be performed is to recognize the disc present in the drive.
The disc recognition procedure involves operations which namely consist of selection of a laser (CD, DVD or BluRay laser) to start disc recognition by way of a substrate thickness measurement, reflection measurement at non-rotating disc, spherical aberration control during disc recognition and initializations, presets, and calibrations of various items such as focus offset, radial tilt, tangential tilt and spherical aberration.
Performing all these operations actually takes a significant amount of time. As timing performance is an important property of an optical drive, the duration and/or number of operations mentioned above should be kept to a minimum.
On the other hand, it is apparent that time could be saved in circumstances where a same disc is still present in the optical drive although the user has given an ejection command but without changing the current disc.
Indeed, under those circumstances, several operations may be skipped such as substrate thickness measurement for selecting the correct laser, spherical aberration adjustment, and radial tilt calibration.
Thus, it can be readily understood that determining whether a same disc is still present in an optical drive may be of the upper importance in assessing the timing performance of an optical drive.
In that context, U.S. Pat. No. 5,974,016 discloses a disc drive equipped with an automatic closing tray wherein a delay is set before the tray is closed, said delay depending on the presence in the tray of an old or a new disc or if the tray is empty. For that purpose, a plurality of sensors at a nest in the tray senses the presence of a disc in the nest and also whether the disc is correctly positioned.
However, it will be appreciated that providing an optical drive with sensors specially dedicated to the determination that a same disc is still present in the drive results in additional costs and technical complexity that are generally hoped to be saved.